Question -
Answer -
Energy flux of sunlight reaching the surfaceof earth, Φ = 1.388 × 103 W/m2
Hence, power of sunlight per squaremetre, P = 1.388 × 103 W
Speed of light, c = 3 × 108 m/s
Planck’s constant, h =6.626 × 10−34 Js
Averagewavelength of photons present in sunlight, 
Number of photons per square metre incidenton earth per second = n
Hence, the equation forpower can be written as:
Therefore, every second, 
photons are incident per square metre on earth.